The present invention relates generally to apparatus for providing a measure of the distance between the apparatus and a remote object and has particular importance in fields of distance determination and automatic focusing of, for example, photographic or television cameras.
Distance determining and automatic focusing arrangements have received considerable attention in recent years. One advantageous type of distance determining automatic focusing apparatus is the spatial image correlation type. Examples of the different forms of arrangements of this type can be found in my U.S. Pat. Nos. 3,836,772; 3,838,275; 3,958,117 and 4,002,899 and in U.S. Pat. No. 3,274,914 by Biedermann, et al.
The typical spatial image correlation apparatus includes two auxiliary optical elements (e.g., lenses or mirrors) and two detector arrays upon which images from a remote object are formed by the optical elements. The object distance is determined by relatively moving one of the auxiliary optical elements so as to change the relative position of the images on the radiation responsive detector arrays until they occupy a critical or correlation position. This position is a measure of the existing object to apparatus distance.
The relative movement of the auxiliary optical element occurs for each distance measuring or focusing operation and the critical condition occurs when there is best correspondence between the radiation distributions of detection images formed on the two detector arrays. This condition of best distribution correspondence results in a unique value or effect in the processed electrical output signals.
In most systems, the relative movement of the auxiliary optical element with respect to the detector array is achieved by moving the lens or mirror relative to one of the detector arrays. The particular position of the element when best distribution correspondence occurs provides a determination of the existing object apparatus distance. In an automatic focusing system, the position of the auxiliary optical element at the time of correlation is used to control the position of a primary optical element such as the taking lens of a camera.
Although distance determining and automatic focusing arrangements of this type have many advantages, they also have some disadvantages. In particular, the required movement of an auxiliary optical element and the accurate determination of the position of the element when correlation occurs leads to considerable mechanical and electrical complexity. It also requires some form of motive means to provide the motion of the auxiliary element. This can create a problem, particularly in automatic focusing cameras where size and weight constraints are critical. The additional complexity and the requirement of some form of motive means increases cost as well as weight and size and increases the likelihood of mechanical failure.
In my U.S. Pat. No. 3,945,023 and in my copending application Ser. No. 696,170, filed June 14, 1976, I describe distance determining and automatic focusing apparatus which does not require a scanning mirror or lens. The outputs of detectors in two detector arrays are compared and processed to provide an indication of distance to an object in terms of one of a plurality of zones. The primary lens is moved to a particular zone depending upon the result of this processing. While these systems do not require a scanning mirror or lens, they become difficult to implement in practice. For example, in Patent No. 3,945,023, the size of the zones for focusing are relatively large which results in low accuracy. While the accuracy of this system may be increased by increasing the number of zones, this results in a large number of detector elements which in turn require more space and results in a much larger and more complex processing circuit. In my copending application, Ser. No. 696,170, I utilize a large number of detector elements in a somewhat less complex processing circuit but still the large number of detectors create considerable difficulty when it is desired to fit them into a reasonably small array, while reduction of individual detector size is possible, when the size of the individual elements becomes small, the output signals therefrom likewise become small and quite difficult to process. Thus, although the size of detectors may be decreased so as to arrange them in satisfactorily small arrays, each decrease in size produces a decrease in output signal and ultimately a point is reached where the size of the signal from the individual detector becomes so small it is masked by noise and becomes too difficult to process.